1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition. More particularly, the present invention relates to a radiation-sensitive resin composition suitable as a material for forming an insulating layer interposed between two integrally laminated sets of conductor wiring in the manufacture of multilayered wiring boards.
2. Prior Art
In recent years, a multilayered wiring board consisting of a number of laminated wiring boards with conductor wiring thereon via insulating layers has become more important in accordance with an increasing demand for a printed wiring board having higher circuit density. As a method for manufacturing such a multilayered wiring board, a method of repeatedly forming an insulating layer on the surface of a wiring board with conductor wiring formed thereon and forming additional conductor wiring electrically conducted to said conductor wiring on said insulating layer (this method may be called a "laminating method") has been proposed. A method which has been proposed to electrically connect two sets of conductor wiring laminated via an insulating layer in this laminating method comprises forming through-holes (holes drilled through an insulating layer) and plating the inner wall surfaces of these through-holes in the same manner as in a laminate-press method. Another method comprises forming drilled holes called via-holes which penetrate specified insulating layers and plating the inner wall surfaces of these via-holes.
As a method for forming these through-holes or via-holes through the insulating layers, a method of using an excimer laser, a method of etching the insulating layers via specified resist patterns by using an appropriate solvent, and the like have conventionally been proposed. In view of productivity, however, these methods were insufficient because a number of holes could not be formed at the same time, or many steps were involved in the production. Moreover, these methods were not satisfactory in view of accuracy of fabrication.
In order to overcome the above problems, a method of using a radiation-sensitive resin composition as a material for forming insulating layers interposed between sets of conductor wiring and forming through-holes on the insulating layers by photolithography has been proposed. According to this method, a number of through-holes can be formed at the same time, thereby ensuring high productivity in the manufacture of multilayered wiring boards. Moreover, since these through-holes can be formed with higher accuracy in comparison with conventional methods, this method is suitably employed in the manufacture of multilayered wiring boards having a minute wiring pattern. The holes formed on the insulating layers formed from a radiation-sensitive resin composition are provided with an electrical path by plating. These holes are called photo-via-holes.
Japanese Patent Application Laid-open No. 273753/1993 has proposed an example of forming an insulating layer by using a phenol resin, amino resin, epoxy resin, and onium salt as the radiation-sensitive resin composition.
Because the laminating method uses a radiation-sensitive resin composition as a material for forming an insulating layer in the manufacture of multilayered wiring boards, this method ensures fabrication of a multilayered laminated structure without using a pressing process and formation of photo-via-holes having a small diameter with high accuracy by photolithography. The laminating method is thus suitable for manufacturing multilayered wiring boards having a minute wiring pattern.
In the manufacture of multilayered wiring boards according to the laminating method, the following properties are required for the radiation-sensitive resin composition used for forming insulating layers:
(1) The resulting insulating layers must exhibit high resolution, whereby photo-via-holes with a small diameter corresponding to minute wiring patterns can be formed with high accuracy and high density;
(2) The resulting insulating layers must exhibit excellent resistance to plating solutions (plating solution resistance) such as an electroless copper plating solution used for forming conductor wiring. Moreover, the resulting insulating layers are required to have superior solvent resistance and excellent waterproofing characteristics after curing;
(3) The surfaces of the resulting insulating layers must exhibit high adhesion to conductor wiring formed by, for example, an electroless copper plating. Here, it is advantageous to roughen the surface of the insulating layer to increase adhesion of the conductor wiring formed on the surface by copper plating. The conductor wiring can be formed on the surface of the insulating layer with higher adhesion by the anchor effect of the roughened surface;
(4) The resulting insulating layers be developed by an alkaline aqueous solution. Undesirable effects on human body or environment can be avoided by using an alkaline aqueous solution as a developer for forming photo-via-holes; and
(5) The resulting insulating layers must exhibit high electrical insulation, which gives rise to high reliability in electrical insulation of the composition, and excellent heat resistance after curing. These properties can ensure the use of the composition for the manufacture of electronic devices which have become smaller and lighter.
However, no conventional radiation-sensitive resin compositions can form insulating layers, while concurrently satisfying the above-described properties.
For example, an insulating layer formed from the radiation-sensitive resin composition disclosed in Japanese Patent Application Laid-open No. 273753/1993 exhibited high alkali developability, high resolution, superior adhesion of conductor wiring by copper plating, and the like. However, it has been pointed out that long-term reliability in electrical insulation of such an insulating layer was adversely affected by an onium salt used as a photoacid generator to a considerable degree.
Accordingly, an object of the present invention is to provide a radiation-sensitive resin composition capable of forming insulating layers exhibiting high resolution, high plating solution resistance, high adhesion to conductor wiring, and developability using an alkaline aqueous solution, producing cured insulating layers with superior solvent resistance, excellent waterproofing characteristics, and high heat resistance. The radiation-sensitive resin composition can produce multilayered wiring boards having high electrical insulation reliability with high efficiency.